This invention relates to the construction of building structures such as walls, beams, girders and the like. Most modern construction systems fall into one of the following broad categories:
1. On-site or pre-manufactured wood and/or metal frame construction. PA1 2. Masonry, joined or assembled at the building site and composed of various materials, including stone, brick, and precast concrete-masonry building units. PA1 3. Manufactured or precast concrete panels. PA1 4. Cast-in-situ concrete structural walls (including composite concrete and insulation material "sandwich" structures and lost-form systems). PA1 5. Tilt-up, cast-on-site concrete walls.
Such systems require mechanical or chemical (bonding) attachment of, or include as components within themselves, environmentally unsafe, if not hazardous, wind and/or vapor barriers, waterproofing and various thermal and acoustic insulation. For example, they generally rely upon pre-manufactured batts or panels for insulation and wind and weatherproofing. Such batts or panels are composed of some or all of: plastic sheeting, kraft paper, aluminum foil, fiberglass, rock wool, petroleum tars, expanded plastics and the like. They require skilled, experienced labor and specialized tools for their construction. They are therefore costly and time consuming to complete. Teaching the skills required to construct these systems is an expensive process, often requiring years of education, formal training and hands-on experience.
Furthermore, many aspects of these systems are environmentally unfriendly; some are even toxic. Wood-based systems require the cutting of large tracts of forest, which is environmentally harmful, and wood is often treated with toxic chemicals to retard combustion, reduce decay or protect against insect infestations. Autoclaved concrete and metal-based systems require large quantities of thermal energy for their manufacture and fabrication. Most commonly used systems further require at least some environmentally harmful, often toxic, moisture and vapor proofing and insulation.
The safety and durability of these systems are also less than ideal. Wood systems are subject to destruction or damage by insects, rot, fire and catastrophic events such as tornadoes, hurricanes and floods. Metal-based, concrete and masonry systems frequently fail at inter-component connecting points during earthquakes or because of soil movement. Complex; e.g. framed systems and most of the composite concrete sandwich, systems are subject to substantial variations in assembly quality and can lead to catastrophic failure if carelessly or incompetently assembled, and they require substantial amounts of costly repair and maintenance.
In addition, all systems, except wood framing, are at best difficult to modify or add onto, requiring considerable skill and specialized tools, making building modifications and additions costly.
Concrete systems must either be permanently encased in, sheathed by, or include internally, air spaces and/or one or more insulation layers such as rigid, expanded plastic foam to reduce thermal or heat transmission through them. However, air spaces and insulating materials reduce the structural integrity of the system, since they vary the compressive and shear strengths across a given section. Moreover, plastics are not porous and consequently do not naturally adhere to or bond intimately with poured concrete. As a consequence, such systems tend to delaminate unless they are permanently secured with mechanical fasteners or adhesives.
An important characteristic of a construction system is the consistency and predictability of its structural qualities. Predictability results from uniformity through any given section of any structural wall constructed under prescribed conditions on any site and at any temperature or humidity. It increases as homogeneity and uniformity throughout the structure are improved. Wood- and steel-framed systems, for example, lack such predictability because their complexities create opportunities for variation in materials, construction quality and workmanship. Concrete systems lack this uniformity and predictability because the strengths, the porosity (affecting bonding within the mixture) and the shapes and sizes of the natural aggregates used in their preparation vary widely from source to source and from one location to another. Completed concrete pours which fail to meet desired strengths must be broken or sawed, removed and replaced, all of which is time consuming and costly.
Further, commonly-employed construction systems eventually exhibit the self-destructive effects resulting from the varying coefficients of thermal and moisture expansion of the differing materials and components employed by them. Ideally, a building wall system should have a uniform coefficient of expansion throughout so that the entire system expands and contracts alike.
Similarly, concrete and concrete/plastic sandwich systems generally cannot be produced at temperatures substantially below the freezing point of water. Very low humidity is also detrimental to the production of consistent, high-quality, cast concrete and to mortar used to bond masonry systems. Ideally, however, building wall systems should be producible regardless of the prevailing temperature or humidity.
Lastly, an increasingly important characteristic of a building wall system is its ability to uniformly "store" thermal energy. This is generally referred to as the wall's thermal mass. Systems that sandwich concrete between layers of rigid plastic foam fail to provide thermal mass because the sides of the sandwich isolate the concrete core, thereby preventing acquisition of heat or cooling from the interior of the structure. Wood-framed structures have a low level of thermal storage capability and, due to their complexities, must be sealed and insulated to prevent thermal loss due to air transfer. Metal-framed structures are insulated on their interior surfaces and consequently have little or no thermal mass. Most concrete and masonry structures are also insulated on their inner surfaces, again, isolating the mass of the wall from thermal input from the interior of the structure. Relatively better thermal mass systems are cast concrete and/or fully-grouted masonry walls, insulated only on their exterior sides. Ideally, a building wall system should provide both low rates of thermal (and acoustic) transmission while simultaneously storing the heat or cooling from within the building. Preferably, such a system does not require the separate application or inclusion of insulation material.
Present construction and building trades practices and literature and current information and literature available from manufacturers and suppliers recommend that fiberglass reinforced cement board panels or plates be used only as sheathing or veneer cladding for frame structures. Practice and literature also specify that, over this sheathing or veneer cladding, various finishes must be applied. In practice and literature, the fiberglass reinforced cement boards are mechanically fastened to wood or metal framing members or to sheathing, decking or sub-flooring that is attached thereto. Once so attached, in both literature and practice, the fiberglass reinforced cement boards act as underlayment for finishes such as tile, elastomeric/foam systems and specialty veneer plasters. Because fiberglass reinforced cement boards are porous and allow ready infiltration of water, they are ordinarily not painted. Since fiberglass reinforced cement boards are also relatively brittle when subjected to point loads and tend to shatter around impact or screw-type penetrations, they are customarily not veneered or further clad with wood or other types of sheet or strip siding materials. Mechanical fasteners simply do not hold well when inserted into such boards without other backing.